Ambient condition detectors have been found to be useful in providing an indication of the presence or absence of the respective condition being detected. Smoke detectors, for example, have been found useful in providing early warning of the presence of airborne particulate matter such as smoke.
Air condition detectors generally have vents that are located within housings, whereby ambient air circulates into and out of the housing in response to movement of the adjacent atmosphere. Heating/Ventilation/Air-conditioning (HVAC)-type duct detectors, alternatively, often sample airflow behind additional internal dust filters, which help to minimize dirt or dust related false alarms. When clean, these filters serve to reduce undesirable dust particles from activating the alarm, while still allowing a steady rate of air to flow through the detection mechanism. However, dust filters periodically and chronically become clogged over time and in such an event, airflow becomes reduced or eliminated.
In other situations, reduced airflow may be due to normal operating conditions and not the result of dust filter contamination. In large commercial buildings, for example, air circulation is often achieved by centralized heating and cooling systems, and the building control systems may be programmed to alter airflow in response to preset schedules. Hence, there may be times of minimal or no circulation, such as during evenings or weekends, which may be falsely indicative of contamination from the filter.
The ability of ambient air condition detectors to operate effectively depends to some degree on the capacity to sample consistent and representative samples of the environmental air. However, in certain scenarios as mentioned above, the ability to sample air becomes compromised as the filters therein become progressively contaminated.
Therefore, there continues to be a need for devices and methods to monitor airflow and allow supervision of internal dust filters by providing a maintenance indication means when the airflow has been reduced due to contamination. It is also desirable to provide an airflow detection arrangement that is able to sample the airflow through the air filter relative to ambient airflow conditions so as to allow for environmental compensation in assessing airflow restriction due to clogged filters.